1. Field of the Invention
The present invention relates to an optical beam pointing system for pointing an irradiation center for radiation when positioning an irradiation target at the irradiation center.
2. Description of the Background Art
Conventionally, radiation therapy is performed by a radiation therapy apparatus, such as a linac (linear accelerator), which irradiates patient lesions with radiation multiple times, thereby destroying abnormal cells, such as cancer cells, while maintaining normal cells.
Before performing radiation therapy, a lesion in a body is located based on diagnostic imaging, such as CT scanning, and the size and range of a radiation target is determined. After the determination, marks for indicating the position to be irradiated with radiation are made on the skin of the patient in order to eliminate the necessity of locating the position to be irradiated with radiation in each irradiation. Normally, there are three marks made by an ink pen or suchlike on the front, left, and right sides of the patient.
For example, as shown in FIG. 13 of Japanese Laid-Open Patent Publication No. 2006-122452, a radiation therapy room is equipped with a radiation therapy apparatus, and three optical beam pointers 93, 94, and 95 disposed in the vicinity of the radiation therapy apparatus, one being on the front side of a patient M laid on a bed 91, the others being disposed in opposition to each other on the left and right sides of the patient. Each of the optical beam pointers 93, 94, and 95 points the irradiation center (aiming center) for the radiation therapy apparatus by projecting a visible light beam passing through the irradiation center.
The patient is positioned such that the irradiation centers pointed by the optical beam pointers are aligned with the irradiation position for radiation, i.e., the visible light beams from the optical beam pointers are respectively incident on the three marks made on the skin of the patient.
As described above, the visible light beams from the optical beam pointers are set so as to pass through the irradiation center for the radiation therapy apparatus. However, in some cases, the visible light beams from the optical beam pointers miss the irradiation center due to some factor such as facility aging or variations in atmospheric conditions. In each such case, maintenance workers have to adjust the projection angles of the optical beam pointers, forcing them to perform troublesome work.
Also, such adjustments require extraordinary subtlety, and therefore may vary from one maintenance worker to another.